addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsWhat is a General Circulation Model (GCM) and What is the Purpose ofDownscaling? General circulation models – Scientific models, also referred to as globalcirculation models, model how the atmosphere, oceans, land surface, and iceinteract to create weather patterns and climate over long periods. Climate modelsare complex and require significant computing power to generate future climatechange projections. Climate modeling at the global scale requires large grids toreduce computational complexity. Downscaling – Increasing the resolution of a large grid to a small grid based onclimatic and topographic gradients. The grid size produced by global modeling istoo large to apply model outputs to the State of California, so downscaling isrequired to produce more accurate (higher resolution) numbers for local regions.Downscaling is like pixels on a television, where a global model is an oldertelevision and downscaling is like a new HD television, represented in Figure 3.6.Figure 3.6Illustration on “Downscaling” in Climate ModelingSource:http://www.accessscience.com/loadBinary.aspx?filename=YB061910FG0020.gif.In view of the uncertainty of the global climate’s responses to increasing GHGemissions and other radiative forcings 4 and the variability amongst models inrepresenting and calculating key processes, it is important to consider resultsfrom several GCMs rather than to rely on just a few. For the 2009 California4 The term “radiative forcing” has been used in the IPCC Assessments with a specifictechnical meaning to denote an externally imposed perturbation in the radiative energybudget of the Earth’s climate system, which may lead to changes in climate parameters.3-10 Cambridge Systematics, Inc.